Internal gear grinding machine

ABSTRACT

An internal gear grinding machine achieves space savings and reduction in size of a machine, as well as prevents the tools from being damaged even when an abnormal situation such as a blackout occurs, by a simplifying dressing operation. The internal gear grinding machine for grinding a workpiece (W) by synchronously rotating the workpiece (W) and a barrel-shaped threaded grinding wheel ( 17 ) in mesh with each other includes a dressing device ( 20 ) for dressing the threaded tool ( 17 ) by meshing the threaded grinding wheel ( 17 ) with a disk dresser ( 56 ). When dressing, the threaded grinding wheel ( 17 ) and the disc dresser ( 56 ) are operated in accordance with the helix angle and barrel shape of the threaded grinding wheel ( 17 ), and the brake mechanism ( 58 ) applies a braking force to a dresser turn drive motor ( 53 ) to enable the disc dresser ( 56 ) to be maintained at a turned position thereof.

TECHNICAL FIELD

The present invention relates to an internal gear grinding machine forgrinding an internal gear with a barrel-shaped threaded tool, andparticularly to an internal gear grinding machine having the dressingfunction of dressing a barrel-shaped threaded tool.

BACKGROUND ART

Heretofore, gear grinding machines have been provided to efficientlyfinish the faces of the teeth of a heat-treated gear by grinding thegear with a threaded grinding wheel, which is a grinding tool. Thesharpness of the threaded grinding wheel decreases due to the wearthereof as grinding is repeated. Accordingly, after a predeterminednumber of gears have been ground, the worn threaded grinding wheel needsto be dressed to restore the sharpness of the faces of the threadsthereof.

For this reason, conventional gear grinding machines have the dressingfunction of dressing a worn threaded grinding wheel with a dresser. Sucha gear grinding machine having the dressing function is disclosed in,for example, Patent Document 1.

On the other hand, of gears, internal gears are frequently used inautomotive transmissions and the like. Recently, there has been a demandfor the improvement of machining accuracy for the purpose of reducingthe vibration and noise of such transmissions. Accordingly, internalgear grinding methods for finish-grinding an internal gear with abarrel-shaped threaded grinding wheel with high accuracy have beenheretofore disclosed, for example, in Non-Patent Document 1.

PRIOR ART DOCUMENTS Patent Document

-   Patent Document 1: Japanese Patent Application Publication No.    2005-111600

Non-Patent Document

-   Non-Patent Document 1: Shigeru Hoyashita, “Barrel Worm-Shaped Tool    with Conjugate Cutting-Edge Profile Generated from Tooth Profile of    Internal Gear [in Japanese],” January, 1996, Transactions of the    Japan Society of Mechanical Engineers C, Vol. 62, No. 593, pp.    284-290

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

In the above-described conventional gear grinding machine, a turningring is turnably supported on the outer periphery of a counter columnstanding upright to face a threaded grinding wheel. Further, a pair ofgrippers each capable of gripping a gear and a dressing device disposedbetween the pair of grippers are provided on the turning ring. Turningthe gripper so that the gripper may face a rotary table capable ofholding a gear allows a gear to be loaded onto and unloaded from therotary table, and turning the dressing device so that the dressingdevice may face the threaded grinding wheel allows dressing to beperformed.

However, in the case where a dressing device for dressing abarrel-shaped threaded grinding wheel for grinding an internal gear isprovided, dressing operation is complex due to limitations associatedwith the shape of an internal gear if this dressing device is justplaced in an internal gear grinding machine. This may increase the sizeof the machine. Moreover, in dressing operation, the threaded grindingwheel and the dresser mesh with each other. When an abnormal situationsuch as a blackout occurs in such a meshing condition, the threadedgrinding wheel, the dresser, and the like may be damaged.

Accordingly, the present invention has been made to solve theabove-described problems, and an object of the present invention is toprovide an internal gear grinding machine which makes it possible toachieve space savings and reduce the size of a machine by simplifyingdressing operation, as well as to prevent the tools from being damagedeven when an abnormal situation such as a blackout occurs.

Means for Solving the Problem

An internal gear grinding machine according to a first invention tosolve the above-described problem is an internal gear grinding machinefor use in grinding a to-be-machined internal gear by synchronouslyrotating the to-be-machined internal gear and a barrel-shaped threadedtool in mesh with each other, the to-be-machined internal gear beingrotatable about a work rotation axis, the barrel-shaped threaded toolbeing rotatable about a tool rotation axis having a predeterminedcrossed axes angle with respect to the work rotation axis, the internalgear grinding machine comprising: dressing means for dressing thethreaded tool with a disk-shaped dresser rotatable about a dresserrotation axis in accordance with a shape of the threaded tool, thedressing means comprising: dresser turning means for turning the dresserabout a dresser pivot perpendicular to the dresser rotation axis; andbraking and maintaining means for applying a braking force to thedresser turning means, and maintaining the dresser at a turned positionthereof.

In an internal gear grinding machine according to a second invention tosolve the above-described problem, is characterized in that the brakingand maintaining means comprises: a rotary shaft disposed coaxially withthe dresser pivot and rotatably supported in a casing; a disk-shapedrotary disk provided on the rotary shaft; a fixing member provided inthe casing to face the rotary disk; an armature disposed between therotary disk and the fixing member and supported to be slidable along therotary shaft; a brake disk disposed on the opposite side of the rotarydisk from the armature; a spring member provided in the fixing member tobias the armature toward the rotary disk; and a coil member provided inthe fixing member to generate a magnetic force when being supplied withpower and thereby attract the armature against a biasing force of thespring member.

In an internal gear grinding machine according to a third invention tosolve the above-described problem, that the dresser turning means is adirect-drive motor comprising: a rotor provided on the rotary shaft; anda stator provided on the casing.

In an internal gear grinding machine according to a fourth invention tosolve the above-described problem, the braking and maintaining meansapplies a braking force to the dresser turning means when the power tothe internal gear grinding machine is shut off.

Effect of the Invention

Accordingly, the internal gear grinding machine according to the presentinvention makes it possible to simplify the entire dressing operation byproviding the braking and maintaining means to the dressing means fordressing the threaded tool with the dresser in accordance with a shapeof the threaded tool, the braking and maintaining means for applying abraking force to the dresser turning means and maintaining the dresserat a turned position thereof. Thus, it is possible to achieve spacesavings and reduce the size of a machine. In addition, the threaded tooland the dresser can be prevented from being damaged even when anabnormal situation such as a blackout occurs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an internal gear grinding machineaccording to one embodiment of the present invention.

FIG. 2 is a perspective view of a dressing device.

FIG. 3 is a partial sectional view of a pivoting unit of the dressingdevice.

FIG. 4 is a front view of the pivoting unit of the dressing device.

Part (a) and (b) of FIG. 5 are detailed views of a brake mechanism. Part(a) of FIG. 5 is a view showing a brake-off state, and part (b) of FIG.5 is a view showing a brake-on state.

FIG. 6 is an external view of a threaded grinding wheel.

FIG. 7 is a vertical cross-sectional view of the threaded grindingwheel.

FIG. 8 is a view showing the threaded grinding wheel which is grinding aworkpiece.

FIG. 9 is a view showing a disc dresser which is dressing the threadedgrinding wheel.

Part (a) to (e) of FIG. 10 are views showing the relationship betweenthe operation of the threaded grinding wheel and the operation of thedisc dresser at the time of dressing. Part (a) of FIG. 10 shows therelationship between an axial position on the threaded grinding wheel atwhich the disc dresser comes into contact with the threaded grindingwheel and the turning angle of the disc dresser about a dresser pivotaxis. Part (b) of FIG. 10 shows the relationship between the axialposition on the threaded grinding wheel at which the disc dresser comesinto contact with the threaded grinding wheel and the rotation angle ofthe threaded grinding wheel about a grinding wheel rotation axis. Part(c) of FIG. 10 shows the relationship between the axial position on thethreaded grinding wheel at which the disc dresser comes into contactwith the threaded grinding wheel and the amount of travel of thethreaded grinding wheel in the direction of the X axis. Part (d) of FIG.10 shows the relationship between the axial position on the threadedgrinding wheel at which the disc dresser comes into contact with thethreaded grinding wheel and the amount of travel of the threadedgrinding wheel in the direction of the Y axis. Part (e) of FIG. 10 showsthe relationship between the axial position on the threaded grindingwheel at which the disc dresser comes into contact with the threadedgrinding wheel and the amount of travel of the threaded grinding wheelin the direction of the Z axis.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an internal gear grinding machine according to the presentinvention will be described in detail with reference to the drawings.

Embodiment

As shown in FIG. 1, a column 12 is supported on a bed 11 of an internalgear grinding machine 1 to be movable in the direction of a horizontal Xaxis. On the column 12, a saddle 13 is supported to be movable up anddown in the direction of a vertical Z axis. On this saddle 13, a turninghead 14 is supported to be turnable about a horizontal grinding wheelpivot axis A. On the turning head 14, a slide head 15 is supported to bemovable in the direction of a horizontal Y axis. This slide head 15 isprovided with a grinding wheel head 16.

On the grinding wheel head 16, a grinding wheel arbor 16 a (see FIG. 8)is supported to be rotatable about a grinding wheel rotation axis B1. Tothe lower end of this grinding wheel arbor 16 a, a barrel-shapedthreaded grinding wheel (threaded tool) 17 is removably attached.Details of this will be described later. Accordingly, driving theturning head 14 and the grinding wheel head 16 causes the threadedgrinding wheel 17 to pivot about a grinding wheel pivot axis A and torotate about the grinding wheel rotation axis B1.

Moreover, on the bed 11, a rotary table 18 is provided in front of thecolumn 12 to be rotatable about a vertical work rotation axis C1. To theupper surface of the rotary table 18, a cylindrical mounting jig 19 isattached. To the inner circumferential surface of the upper end of thismounting jig 19, a workpiece W which is a to-be-machined internal gearis removably attached. Accordingly, driving the rotary table 18 causesthe workpiece W to rotate about the work rotation axis C1.

Furthermore, a dressing device 20 is provided at a side of the rotarytable 18 with respect to the direction of the Y axis. To this dressingdevice 20, a disk-shaped disc dresser 56 for dressing the threadedgrinding wheel 17 is removably attached. It should be noted that thecolumn 12, the saddle 13, the turning head 14, the slide head 15, thegrinding wheel head 16, the dressing device 20 constitute dressingmeans, and a dresser turn drive motor (dresser turning means) 53 to bedescribed later.

As shown in FIGS. 1 and 2, the dressing device 20 includes a base unit31 provided on the bed 11, and a pivoting unit 32 provided on this baseunit 31. The base unit 31 includes a fixing portion 41 and a rotatingportion 42. The fixing portion 41 is fixed to the upper surface of thebed 11. The rotating portion 42 is supported on the fixing portion 41 tobe rotationally indexable about a vertical dresser advance/retreat axisC2. Further, the base end of the pivoting unit 32 is supported on acentral portion of the upper surface of the rotating portion 42. In anend portion of this pivoting unit 32, a disc dresser 56 is attached.

Accordingly, in the dressing device 20, rotating the rotating portion 42with respect to the fixing portion 41 of the base unit 31 causes thepivoting unit 32 to pivot about the dresser advance/retreat axis C2.Thus, the disc dresser 56 can advance or retreat between a dressingposition P2 where the disk dresser 56 can dress the threaded grindingwheel 17 and a retreat position P1 where the disk dresser 56 retreatsfrom the dressing position P2 at the time of grinding.

Next, the configuration of the pivoting unit 32 of the dressing device20 will be described in detail with reference to FIGS. 2 to 5.

As shown in FIGS. 2 to 4, a cylindrical housing portion (casing) 51 isformed in an end portion of the pivoting unit 32. In the housing portion51, a rotary shaft 52 is housed to be rotatable about a horizontaldresser pivot axis B2 with a plurality of bearings interposedtherebetween. Further, the direct-drive dresser turn drive motor(dresser turning means) 53 is interposed between the housing portion 51and the rotary shaft 52.

This dresser turn drive motor 53 includes a stator 53 a at an outerposition and a rotor 53 b disposed radially inward of this stator 53 a.While the stator 53 a is fixed on the inner circumferential surface ofthe housing portion 51, the rotor 53 b is fixed on the outercircumferential surface of the rotary shaft 52. In other words, therotor 53 b rotates with respect to the stator 53 a by driving thedresser turn drive motor 53, so that the rotary shaft 52 can rotate withrespect to the housing portion 51.

Moreover, a dresser rotational drive motor 55 is supported on one end ofthe rotary shaft 52 with a support member 54 interposed therebetween.The output shaft of this dresser rotational drive motor 55 is rotatableabout a dresser rotation axis C3, and the disc dresser 56 is attached tothis output shaft. Accordingly, driving the dresser turn drive motor 53and the dresser rotational drive motor 55 causes the disc dresser 56 toturn about the dresser pivot axis B2 and to rotate about the dresserrotation axis C3.

It should be noted that the dresser pivot axis B2 and the dresserrotation axis C3 are disposed perpendicular to each other, and thisdresser pivot axis B2 is located to pass through the inside of the edge(faces) of the blade of the disc dresser 56 attached to the dresserrotational drive motor 55. In other words, the installation position ofthe disc dresser 56 is set such that the dresser pivot axis B2 passesthrough the inside of the edge of the blade thereof when the discdresser 56 is attached to the dresser rotational drive motor 55.

On the other hand, to the other end of the rotary shaft 52, an encoder57 is connected on the outside of the housing portion 51. Thus, wheneverthe rotary shaft 52 rotates, the rotation angle thereof is detected bythe encoder 57. Further, a brake mechanism (braking and maintainingmeans) 58 which can stop the rotation of this rotary shaft 52 isprovided between the other end of the rotary shaft 52 and the housingportion 51.

As shown in part (a) of FIG. 5, the brake mechanism 58 includes a rotarydisk 71 on the rotary shaft 52 side and fixing members 72 on the housingportion 51 side. The rotary disk 71 is formed into the shape of a disk,and is keyed to the rotary shaft 52. Moreover, the fixing members 72 aredisposed radially outward from the rotary shaft 52 at regular intervalsin the circumferential direction thereof. While one ends of the fixingmembers 72 are fixed to the inner circumferential surface of the housingportion 51, other ends thereof can slidably contact the outercircumferential surface of the rotary shaft 52.

In each of these fixing members 72, a coil 73, a spring 74, and asupport pin 75 are buried. The coil 73 is supplied with power togenerate a magnetic force when the power of the internal gear grindingmachine 1 is turned on. The spring 74 generates a biasing force in theaxial direction (direction of the dresser pivot axis B2) of the rotaryshaft 52 toward the outside of the fixing member 72 by one end thereofbeing supported in the fixing member 72.

To the outside of the rotary shaft 52, a disk-shaped armature 76 isfitted. The peripheral portion of this armature 76 is slidably supportedby the support pins 75. The armature 76 is disposed in contact with theother ends of the springs 74. The support pins 75 further support abrake disk 77. Specifically, the rotary disk 71 fixed to the rotaryshaft 52 is disposed to be interposed between the armature 76 and thebrake disk 77 in the axial direction of the rotary shaft 52.

Accordingly, when the coils 73 are supplied with power, magnetic forcesare generated in these coils 73, and therefore the armature 76 isattracted by the coils 73 against the biasing forces of the springs 74as shown in part (a) of FIG. 5. Thus, a gap is formed between the rotarydisk 71 and each of the armature 76 and the brake disk 77. As a result,the rotation of the rotary shaft 52 is permitted.

On the other hand, when the supply of power to the coils 73 is stopped,the magnetic forces of these coils 73 disappear, and therefore thearmature 76 is slid toward the rotary disk 71 by the biasing forces ofthe springs 74 as shown in part (b) of FIG. 5. Thus, the rotary disk 71is pressed against the brake disk 77 by the armature 76. As a result,the rotation of the rotary shaft 52 is stopped.

Moreover, an unillustrated coolant supply system is provided in theinternal gear grinding machine 1. Coolant supplied from this coolantsupply system is jetted toward a portion of the threaded grinding wheel17 which is machined by the disc dresser 56 at the time of dressing.Thus, as shown in FIGS. 3 and 4, a coolant injection tip 59 for jettingthe coolant is supported on the pivoting unit 32 of the dressing device20.

As shown in FIG. 8, the workpiece W to be ground by the internal geargrinding machine 1 has workpiece specifications from which apredetermined tooth profile can be obtained. The tooth profile is givena predetermined helix angle. On the other hand, as shown in FIGS. 6 and7, the threaded grinding wheel 17 for grinding the workpiece W is formedinto a barrel shape to have grinding wheel specifications whichappropriately mesh with the workpiece specifications. The threads of thethreaded grinding wheel 17 are given a predetermined helix angle.Specifically, the threaded grinding wheel 17 is formed into a barrelshape which has a diameter dimension gradually decreasing from anaxially intermediate portion thereof toward axially opposite endportions thereof. The axial length (grinding wheel widthwise length) ofthe threaded grinding wheel 17 is a length h.

In the internal gear grinding machine 1, when the workpiece W is groundwith the threaded grinding wheel 17, for the purpose of increasinggrinding speed by increasing the relative velocity (slip velocity)occurring between the workpiece W and the threaded grinding wheel 17,the grinding wheel rotation axis B1 of the threaded grinding wheel 17can be turned to intersect the work rotation axis C1 of the workpiece Wat a predetermined crossed axes angle (hereinafter referred to as ashaft angle Σ). In other words, the threaded grinding wheel 17 rotatesabout the grinding wheel rotation axis B1 intersecting the work rotationaxis C1 of the workpiece W at the shaft angle Σ. Accordingly, formingthe threaded grinding wheel 17 into a barrel shape enables the threadedgrinding wheel 17 installed at the shaft angle Σ to be meshed with theworkpiece W.

Next, grinding and dressing operations of the internal gear grindingmachine 1 will be described in detail with reference to FIGS. 2, 5, 6,and 8 to 10.

The grinding of the workpiece W with the internal gear grinding machine1 starts with attaching the workpiece W to the mounting jig 19.Subsequently, the threaded grinding wheel 17 is moved in the directionsof the X, Y, and Z axes by driving the column 12, the saddle 13, theturning head 14, and the slide head 15, and turned about the grindingwheel pivot axis A so as to be tilted at the shaft angle Σ correspondingto the helix angle of the workpiece W, thus being placed at the insideof the workpiece W.

Then, by driving the column 12, the threaded grinding wheel 17 is movedin the direction of the X axis (to the left in FIG. 1) to be meshed withthe workpiece W (see FIG. 8). After that, the grinding wheel head 16 isdriven to rotate the threaded grinding wheel 17 about the grinding wheelrotation axis B1, and the rotary table 18 is driven to rotate theworkpiece W about the work rotation axis C1. Subsequently, the threadedgrinding wheel 17 is moved up and down in the direction of the Z axiswhile being moved in the direction of the X axis by further driving thecolumn 12 and the saddle 13. This causes the threaded grinding wheel 17to cut into the workpiece W. As a result, the faces of the teeth of theworkpiece W are ground by the faces of the threads of the threadedgrinding wheel 17.

It should be noted that the meshing position of the threaded grindingwheel 17 with the workpiece W at the time of grinding is a contact(meshing) line 17 a such as shown in FIG. 6. In other words, in thegrinding of the workpiece W with the threaded grinding wheel 17, aplurality of thread faces of the threaded grinding wheel 17 grind aplurality of tooth faces of the workpiece W at the same time.

What should be noted here is that the use of the threaded grinding wheel17 to grind a certain number of workpieces W causes a decrease insharpness of the threaded grinding wheel 17 due to the wear of the facesof the threads thereof. To address this decrease, the dressing of thethreaded grinding wheel 17 with the disc dresser 56 needs to be carriedout on a regular basis.

The dressing of the threaded grinding wheel 17 with the disc dresser 56starts with driving the base unit 31 of the dressing device 20 to rotatethe rotating portion 42 with respect to the fixing portion 41. Thus, asshown in FIG. 2, the pivoting unit 32 pivots about the dresseradvance/retreat axis C2, and the disc dresser 56 pivots by 90 degreesfrom the retreat position P1 to the dressing position P2.

Subsequently, the dresser turn drive motor 53 is driven to turn the discdresser 56 about the dresser pivot axis B2 in accordance with the helixangle of the threaded grinding wheel 17, thus positioning the discdresser 56. At this time, since the power to the internal gear grindingmachine 1 is on, the coils 73 of the brake mechanism 58 are suppliedwith power, and the armature 76 is attracted by the coils 73 against thebiasing forces of the springs 74 as shown in part (a) of FIG. 5. As aresult, the rotation of the rotary disk 71 is permitted. Thus, abrake-off state is established, and the rotary shaft 52 is allowed torotate.

On the other hand, the column 12, the saddle 13, and the slide head 15are driven to move the threaded grinding wheel 17 in the directions ofthe X, Y, and Z axes so that the threaded grinding wheel 17 may face, inthe direction of the Y axis, the disc dresser 56 disposed at thedressing position P2. It should be noted that during the above-describedmoving of the threaded grinding wheel 17 in a setup for grinding, thethreaded grinding wheel 17 is turned by driving the turning head 14 sothat the grinding wheel rotation axis B1 may extend in the verticaldirection, and the turning angle (shaft angle Σ) is zero degrees.

Subsequently, by driving the slide head 15, the threaded grinding wheel17 is moved in the direction of the Y axis to be meshed with the discdresser 56 placed at the dressing position P2 (see FIG. 9). Further, inthe above-described meshing state, by driving the column 12, the saddle13, the slide head 15, and the grinding wheel head 16 in accordance withthe helix angle and barrel shape of the threaded grinding wheel 17, thethreaded grinding wheel 17 is rotated about the grinding wheel rotationaxis B1, moved in the directions of the X and Y axes, and at the sametime moved up and down in the direction of the Z axis over the length h.Also, by driving the dresser turn drive motor 53 and the dresserrotational drive motor 55, the disc dresser 56 is turned about thedresser pivot axis B2 and rotated about the dresser rotation axis C3.

This causes the disc dresser 56 to cut into the threaded grinding wheel17. As a result, the faces of the threads of the threaded grinding wheel17 are dressed by the faces of the blade of the disc dresser 56. Thisdressing operation is performed a number of times equal to the number ofthread grooves of the threaded grinding wheel 17. It should be notedthat at the time of dressing, coolant is jetted from the coolantinjection tip 59 toward the portion of the threaded grinding wheel 17which is being machined by the disc dresser 56.

When the dressing operation is finished, the disc dresser 56 is pivotedfrom the dressing position P2 to the retreat position P1 to be broughtto a waiting state, and a predetermined number of workpieces W areground with the threaded grinding wheel 17 after dressing. Then, such aseries of operations are repeated.

Next, the relationship between the movement of the threaded grindingwheel 17 and the movement of the disc dresser 56 at the time of theabove-described dressing will be described in detail with reference topart (a) to (e) of FIG. 10.

First, part (a) of FIG. 10 shows the relationship between an axialposition on the threaded grinding wheel 17 at which the disc dresser 56comes into contact with the threaded grinding wheel 17 and the turningangle of the disc dresser 56 about the dresser pivot axis B2. Therelationship therebetween can be approximately represented by aquadratic curve which is convex downward. Specifically, the turningangle of the disc dresser 56 is set to decrease to a minimum when themeshing position of the disc dresser 56 is at the axially intermediateportion of the threaded grinding wheel 17, and to gradually increase asthe meshing position of the disc dresser 56 moves toward an upper orlower end portion of the threaded grinding wheel 17 with respect to theaxial direction thereof. The reason for the above-described setting isthat since the threaded grinding wheel 17 is in a barrel shape, thehelix angle thereof increases from the axially intermediate portionthereof toward the axially opposite end portions thereof, and theturning angle of the disc dresser 56 also increases accordingly.

Part (b) of FIG. 10 shows the relationship between the axial position onthe threaded grinding wheel 17 at which the disc dresser 56 comes intocontact with the threaded grinding wheel 17 and the rotation angle ofthe threaded grinding wheel 17 about the grinding wheel rotation axisB1. The relationship therebetween can be approximately represented by astraight line. Specifically, the rotation angle of the threaded grindingwheel 17 is set to gradually increase in a clockwise direction as themeshing position of the disc dresser 56 moves toward the upper endportion of the threaded grinding wheel 17 with respect to the axialdirection thereof, and to gradually increase in a counterclockwisedirection as the meshing position of the disc dresser 56 moves towardthe lower end portion of the threaded grinding wheel 17 with respect tothe axial direction thereof.

Part (c) of FIG. 10 shows the relationship between the axial position onthe threaded grinding wheel 17 at which the disc dresser 56 comes intocontact with the threaded grinding wheel 17 and the amount of travel ofthe threaded grinding wheel 17 in the direction of the X axis. Therelationship therebetween can be approximately represented by a cubiccurve. Specifically, the amount of travel of the threaded grinding wheel17 in the direction of the X axis is set to gradually increase in thedirection in which the grinding wheel rotation axis B1 moves toward thework rotation axis C1 as the meshing position of the disc dresser 56moves toward the upper end portion of the threaded grinding wheel 17with respect to the axial direction thereof, and to gradually increasein the direction in which the grinding wheel rotation axis B1 moves awayfrom the work rotation axis C1 as the meshing position of the discdresser 56 moves toward the lower end portion of the threaded grindingwheel 17 with respect to the axial direction thereof. More specifically,the amount of travel of the threaded grinding wheel 17 in the directionof the X axis is point-symmetric about the point at which the axialposition on the threaded grinding wheel 17 at which the disc dresser 56comes into contact with the threaded grinding wheel 17 is the axiallyintermediate portion of the threaded grinding wheel 17. The amount oftravel of the threaded grinding wheel 17 in the direction of the X axisvaries slowly when the meshing position of the disc dresser 56 is nearthe axially intermediate portion, varies greatly when the meshingposition starts moving from the axially intermediate portion toward theaxially opposite end portions, and varies slowly when the meshingposition comes near the axially opposite end portions.

Part (d) of FIG. 10 shows the relationship between the axial position onthe threaded grinding wheel 17 at which the disc dresser 56 comes intocontact with the threaded grinding wheel 17 and the amount of travel ofthe threaded grinding wheel 17 in the direction of the Y axis. Therelationship therebetween can be approximately represented by aquadratic curve which is convex upward. Specifically, the amount oftravel of the threaded grinding wheel 17 in the direction of the Y axisis set to increase to a maximum in the direction in which the grindingwheel rotation axis B1 moves away from the dresser rotation axis C3 whenthe meshing position of the disc dresser 56 is at the axiallyintermediate portion of the threaded grinding wheel 17, and to graduallyincrease in the direction in which the grinding wheel rotation axis B1moves toward the dresser rotation axis C3 as the meshing position of thedisc dresser 56 moves toward the upper or lower end portion of thethreaded grinding wheel 17 with respect to the axial direction thereof.The reason for the above-described setting is that since the threadedgrinding wheel 17 is in a barrel shape, the diameter dimension thereofgradually decreases from the axially intermediate portion thereof towardthe axially opposite end portions thereof, and the depth of the cut bythe disc dresser 56 also gradually increases accordingly.

Part (e) of FIG. 10 shows the relationship between the axial position onthe threaded grinding wheel 17 at which the disc dresser 56 comes intocontact with the threaded grinding wheel 17 and the amount of travel ofthe threaded grinding wheel 17 in the direction of the Z axis. Therelationship therebetween can be approximately represented by a straightline. Specifically, the amount of travel of the threaded grinding wheel17 in the direction of the Z axis is set to gradually increasevertically downward as the meshing position of the disc dresser 56 movestoward the upper end portion of the threaded grinding wheel 17 withrespect to the axial direction thereof, and to gradually increasevertically upward as the meshing position of the disc dresser 56 movestoward the lower end portion of the threaded grinding wheel 17 withrespect to the axial direction thereof.

Accordingly, operating the threaded grinding wheel 17 and the discdresser 56 in accordance with the helix angle and barrel shape of thethreaded grinding wheel 17 as described above causes the faces of theblade of the disc dresser 56 to come into contact with thread faces ofthe threaded grinding wheel 17 similar to tooth surfaces of theworkpiece W, which come into contact (mesh) therewith along the contactline 17 a, and to perform dressing.

Moreover, since the dresser turn drive motor 53 is a direct-drive motor,a backlash can be suppressed unlike in the case of a motor using a gear.This enables the disc dresser 56 to turn continuously and smoothly.Also, since the encoder 57 is connected to this dresser turn drive motor53, the disc dresser 56 can be positioned with high accuracy withrespect to the helix angle of the threaded grinding wheel 17.

Furthermore, since the coolant injection tip 59 is provided on thepivoting unit 32 of the dressing device 20 for advancing and retreatingthe disc dresser 56, when the disc dresser 56 is placed at the dressingposition P2, the coolant injection tip 59 is also placed at apredetermined position. This eliminates the necessity of adjusting theposition of the coolant injection tip 59 at the time of dressing.

It should be noted that in the case where an abnormal situation such asa blackout occurs during the use (driving) of the internal gear grindingmachine 1 to cause the shutting off of the power thereof, the armature76 is slid toward the rotary disk 71 by the biasing forces of thesprings 74 as shown in part (b) of FIG. 5, because the supply of powerto the coils 73 of the brake mechanism 58 is stopped and the magneticforces of these coils 73 disappear. Thus, the rotary disk 71 is pressedagainst the brake disk 77 by the armature 76 to be brought to a state inwhich the brake is ON, thus stopping the rotation of the rotary shaft52.

As a result, the turning of the disc dresser 56 caused by the coastingof the dresser turn drive motor 53 and an imbalance in the installationposition of the dresser rotational drive motor 55 is stopped, and,further, the disc dresser 56 is maintained in that state. This reducescareless contact between the threaded grinding wheel 17 and the discdresser 56, and prevents damage to the threaded grinding wheel 17 andthe disc dresser 56.

In the above-described dressing device 20, the dressing position P2 ofthe disc dresser 56 is set to face the threaded grinding wheel 17 to bedressed in the direction of the Y axis. However, this dressing positionP2 may also be set to face the threaded grinding wheel 17 to be dressedin the direction of the X axis. In the case of such a configuration,dressing can be performed by replacing the movement of the threadedgrinding wheel 17 and the disc dresser 56 in the direction of the X axiswith that in the direction of the Y axis.

Accordingly, in the internal gear grinding machine according to thepresent invention, by operating the threaded grinding wheel 17 and thedisc dresser 56 in accordance with the helix angle and barrel shape ofthe threaded grinding wheel 17 at the time of dressing, and the brakemechanism 58 applies a braking force to the dresser turn drive motor 53to enable the disc dresser 56 to be maintained at a turned positionthereof. Thus, the entire dressing operation is simplified, and theoperating range thereof can be reduced to a minimum. Thus, it ispossible to save the space occupied by the dressing device 20 and reducethe size thereof. As a result, the entire size of the internal geargrinding machine 1 can be reduced. Moreover, when an abnormal situationsuch as a blackout occurs, the turning of the disc dresser 56 isimmediately stopped. This can reduce careless contact between thethreaded grinding wheel 17 and the disc dresser 56, and can thereforeprevent damage to the threaded grinding wheel 17 and the disc dresser56.

Moreover, the dresser turn drive motor 53 is a direct-drive motor andtherefore backlashless. This enables the disc dresser 56 to turncontinuously and smoothly. Accordingly, the disc dresser 56 can beturned clockwise or counterclockwise by a very small turning amount.Also, since the encoder 57 is connected to this dresser turn drive motor53, the disc dresser 56 can be positioned with high accuracy withrespect to the helix angle of the threaded grinding wheel 17.

INDUSTRIAL APPLICABILITY

The present invention can be implemented to an internal gear grindingmachine including a dressing device which can restore the grinding wheelwith high accuracy.

The invention claimed is:
 1. An internal gear grinding machine for usein grinding a to-be-machined internal gear by synchronously rotating theto-be-machined internal gear and a barrel-shaped threaded tool in meshwith each other, the to-be-machined internal gear being rotatable abouta work rotation axis, the barrel-shaped threaded tool being rotatableabout a tool rotation axis having a predetermined crossed axes anglewith respect to the work rotation axis, the internal gear grindingmachine comprising: dressing means for dressing the threaded tool with adisk-shaped dresser rotatable about a dresser rotation axis inaccordance with a shape of the threaded tool, the dressing meansincluding: dresser turning means for turning the dresser about a dresserpivot perpendicular to the dresser rotation axis; and braking andmaintaining means for applying a braking force to the dresser turningmeans, and maintaining the dresser at a turned position thereof, thebraking and maintaining means including: a rotary shaft disposedcoaxially with the dresser pivot and rotatably supported in a casing; adisk-shaped rotary disk provided on the rotary shaft; a fixing memberprovided in the casing and opposing the rotary disk; an armaturedisposed between the rotary disk and the fixing member and supported tobe slidable along the rotary shaft; a brake disk disposed at a sideopposite to the armature with respect to the rotary disk; a springmember provided in the fixing member to bias the armature toward therotary disk; and a coil member provided in the fixing member to generatea magnetic force when being supplied with power and thereby attract thearmature against a biasing force of the spring member.
 2. The internalgear grinding machine according to claim 1, wherein the dresser turningmeans is a direct-drive motor comprising: a rotor provided on the rotaryshaft; and a stator provided on the casing.
 3. The internal geargrinding machine according to claim 1, wherein the braking andmaintaining means applies a braking force to the dresser turning meanswhen power to the internal gear grinding machine is shut off.